1. Field of the Invention
The present invention relates to a cooling means for the squish part, namely, the wall part over the squish area formed underthe cylinder head of an air cooling over head valve engine, which involves a fan in front thereof, and a wind tunnel for cooling the squish part.
2. Related Art
A cooling means for the squish part of an air cooling over head valve engine is well known to those who are skilled in the art.
Such cooling means comprises a fan disposed in front of the engine for generating cooling wind; a fan case which covers the front side of the fan and the engine; a wind tunnel formed through the cylinder head of the engine near the squish area for passing a part of cooling wind generated by the fan; and a baffle plate fixed to the interior surface of the fan case for guiding cooling wind blown up from the fan to the wind tunnel so that the squish area of the engine is cooled by the wind passing through the wind tunnel.
However, the baffle plate is made separately and then welded to the fan case. Thus, the number of parts is increased, and the forming and welding of the plate takes excessive time, so that manufacturing cost is expensive. Moreover, the resonance of the baffle plate with the engine may bring about sounding and fracture from fatigue.
Moreover, in a known cooling means of the squish area, another baffle plate is disposed for dividing cooling wind into two directions namely, to the wind path around the whole cylinder including the wind tunnel.
However, this baffle plate located about at the boundary between the cylinder and the cylinder head is elongated inside of the fan case therefrom, reducing the sectional area of the wind path to the cylinder head. As such, a smaller volume of cooling wind is delivered to the wind path behind the plate, and that a strain on the cylinder head may arise from the insufficiency of the cooling. Moreover, the insufficiency of the cooling may result in accumulation of heat at the squish part and the combustion chamber, causing preignition, and knocking. Consequently, the engine may not be suitable for conditions with high combustion temperatures, such as high speed running, or high compression ratio. And, sounding and fracture from fatigue of this plate may be brought only by the resonance thereof, too.
As described in Japanese Utility Model Issue Sho 59-5130, such a wind tunnel has a bottom surface with a stair graded up above the squish area. Thus the thickness of the cylinder head is decreased at the stair part, and the amount of the heat accumulated at the stair part becomes larger to invite preignition and knocking.